1. Field of the Invention
The present invention relates to a process unit which contains an image bearing member and all or a part of process means which acts on the image bearing member, and which is detachably mountable to a main body of an apparatus, and also to an image forming apparatus using such a process unit.
2. Description of the Prior Art
The prior art will be described with respect to an electrophotographic copying apparatus, as an example of the image forming apparatus.
Conventionally, electrophotographic machines require a trained and expert serviceman for replacement of a photosensitive member which is an image bearing member, supply of the developer, disposal of the used developer, cleaning of charging wires, replenishment and adjustment of various parts and so on. It is needed that the serviceman goes to offices having the electrophotographic machines, whenever the servicing is necessary. This is disadvantageous both for machine makers and machine users, since the makers have to establish and maintain the servicing network to meet the demand, and the users have to wait for the serviceman to arrive before the restart of the machine operation.
To remove those disadvantages, it is recently proposed, as disclosed in U.S. Pat. No. 3,985,436, that various process means, such as a photosensitive member, a developing device, a cleaning means and a charger are all contained in a casing as a unit, and that the unit is replaced with a fresh unit when the unit set in the machine is no longer usable, so that all the means contained therein are exchanged simultaneously, thus saving the machine servicing operation. This makes it possible for users to replace various elements without resort to an expert serviceman and eliminates the necessity of periodical maintenance work. Also, the serviceman's job can be tremendously reduced. Additionally, the process unit can contain a developer of a different color, which allows for the users to take a copy with the different color. Another process unit can replace to use the type of developing means which suits the original to be copied. Those are additional advantages.
However, this type of process unit involves a problem that, when the unit is replaced, or when the unit is kept out of the image forming apparatus, the photosensitive member contained in the process unit is possibly stained by a hand of the user, or the photosensitive member is possibly damaged mechanically or physically, if it is partly exposed. In addition, the photosensitive layer of zinc oxide, selenium or organic photoconductor (opc), which constitutes the image bearing member in the process unit, may be deteriorated, when it is exposed to the external light. The stain, damage or deterioration will adversely affect the image formed by the image forming apparatus with the process unit.
The process unit is relatively frequently placed into or out of the image forming apparatus during its service life, since it is replaced with another unit of different color copy, for example, as described hereinbefore, so that it is desirable to ensure the protection of the photosensitive member.